Fast acting solenoid



Jan. 10, 1961 R. w. DANKLEFS 2,967,983

FAST ACTING SOLENOID Filed Jan. 3, 1958 l gag/I Z INVENTOR.

% mam ATTORNEYJ United 2,967,983 Patented Jan. 10, 196i Fice ' FAST ACTING SO LENOID Ronaid W. 'Danklefs,-1asadena, Calif assignor to Bur; troughs Corporation,-Detroit, :.Mich.,acorporation or Michigan Filed Jan. 3, 1958,"Ser. N0. 706-,977 3 Claims. (Cl.'31 7189) This invention relates to magnetically operated switch devices and more particularly 'toithe typeknown. as solenoids. v v

in the field of magnetically operatedswitch"devices it is highly desirable in many applicationsto secureve-ry fast switch actuation. In order to secure high speed actuation resort has been made to 'severaltechniques. One technique involves the use of two'windingsfthe first of which has a small number of turns and the "second a large number of turns. A large currentthrough the first winding provides a rapid build up of a'magnetic'field which operates anauxiliary switch to connectthesecond winding in series with the first. The magnetic'field establi hed by the two windings aid each'otherto establish'a rapidly increasing large magnetic field which operates a switch device. Another technique'invo-lves using a condenser in conjunction with-a winding to securea large surge ot current initially and thereby'build-upvery rapidly a magnetic field whichactuatesaswitch 'device. These and other techniques which rely on the energizatiomofa winding and the build up of a magnetic field to operate a switch mechanism necessarily involve a time lag between the application of currentto-the actuating winding and the operation of the switch device. It is a feature of this invention to minimize the time lag involved in magnetically operated switchmechanisms such as solenoids'or the like and yet provide a suitable device wh-ich is-relatively simple in operation,=inexpensivetomanufacture and very reliable.

According to one arrangement--of the-prese'nt invention a fast acting solenoidis provided which-includes a-casing, made of a material that has high permeability and low retentivity, disposed between first and second disc members, also made of a material thathas high permeability and low retentivity. Both disc members are mo'unted on a rod-like member and "spaced a given distance-from one another. The first and second-discs andtheir interconnecting rod-like member may assume either of two stationarypositions. A plunger:isimovably'mounted on the interconnecting rod between the two discs, and first and second springs are disposed between the movable plunger and the respective first and second discs. First and second coils, each having 'a core, are located in opposite ends of the casing andwhenenergized serve to magnetize adjacent portions of the 'casing and the associated disc. A source of power and a control switch device is provided for selectively energizing either of the two coils. With the control switch :plaeed in a first position, the first coil is energized and a magnetic field is established in adjacent portions of the casing, the first disc and the plunger. Consequently the 'first disc and the plunger are magneticallypolarized and drawn toward each other by the force of magnetic attraction, compressing the first spring therebetween. The first disc, second disc and interconnecting rod assume one of their bi-stable stationary positions. If the switch device is changed to a second position, thefirst coil is de-enerized as the second coil is energized. The 'first spring undergoes decompression and rapidly moves the first dis c, the second disc and the-interconnecting rod to a second one of their bi-stable stationary positions. Immediately there- 'after the magnetic field from thesecond coil builds up and provides a magnetic force of attraction that holds the second disc in the second stationary position, draws the movable plunger toward the second disc and compresses the second spring therebetween. As the magnetic field fromthe' second coil builds'up, a strong magnetic force of attraction is established between the casing and 'the'secon'd'disc. This force of magnetic attraction issufficiently strong to' prevent the second disc from bouncing back and forth against the casing. Each time the control switch is changed in position, the firstand second discs and the interconnecting'rod rapidly change from one stable stationary ."position to another stable stationary position, and 'in a follow-up operation'immediately thereafter the magnetically polarized plunger and disc are drawn toward each other, thereby compressing the associated spring therebetween. it is the follow-up action in each instance of compressing the associated spring and holding it in compression that makes possible the rapid movement of the rod and associated discs to their new position when the control switch is operated to a new position.

Theseand otherfeatures of this invention may be more fully appreciated when considered in the light of the following specification and drawings in which:

Fig. 1 illustrates in cross section a fast acting solenoid according to'this invention with the switch mechanism shown in meet its two-stable stationary positions;

Pig. 2 is an electrical diagram showing how the device in Fig. 1 may be energized;

Fig. 3 is a cross-sectional view like that in Fig. 1 with the switch mechanism shown in the second of its two stable stationary positions.

"Reference is made to Fig. 1 for a detailed description ofa fast acting solenoid according to this invention. The assembly includes a cylindrical casing composed of two parts it and 12, made of soft iron or other material of high permeability and low retentivity, separated by a flat annular member 14 made of any material which has low permeability. End collars dead 18 aresuitably secured to the cylindrical portions 10 and 12 as by bolts 20 and 22 running longitudinally within the casing. Cores 24 and 2-3 are disposed within the respective collars 16 and The cores are separated from their'respective collars by cylindrical sleevesZS and 34 Each collar and core is made of material that has high permeability and low retentivity while each cylindrical sleeve is made of material that has low permeability. Each collar and its associated cylindrical sleeve and core are formed into a unitary structure. Coils 32 and 34 are wound on spools 36 and 38 disposed on respective cores 24 and 26.

Portions id and' tZ of the cylindrical sections '10 and 32 extend inwardly as shown. .A bushing 44 and pins 4-6 and 4:; are press fitted within the inwardly projecting portions db and 42. A plunger 50 is loosely journalled within the bushing A rod 52 extends through a hole in the plunger 5%, and each is free to move with respect to the other. The end of the rod 52 threadedly engages disc members 5? and 56, a pair of locking nuts 58 and 60 being provided to firmly secure the disc members in position. The gap between the disc members 54 and 56 and the associated cores 24 and 26 may be increased or diminished by adjusting the position of the disc members on the corresponding threaded portions of the rod 52. A pair of springs 62 and 64 are disposed about the rod 52 within bores formed in respective cores 24 and 26.

The fast acting solenoid illustrated in Fig. "I is connected in a circuit arrangementsuch as indicated in Fig. 2. The coils in Fig. 2 corresponding to the'coils 32 and 3 3 in Fig. 1 are labeled with like numbers. A battery 70 or other source of DC. power is coupled through a pair of resistors 72 and 74 to respective contacts 76 and 78 of a control switch 79. Condensers 8t and 82 are coupled across respective resistors 72 and 74 to provide a large surge of current for reasons hereinafter explained. A pair of resistors 84 and 86 are connected between ground and respective contacts 88 and 96 of the switch 79. When a switch arm 92 is thrown to the left position, as indicated, the coil 32 is energized, and when the switch arm 32 is thrown to the right position, engaging the contacts and 90, the coil 34 is energized. While the control switch '79 is illustrated as a mechanical switch, it is to be understood that the switch may be auy one of various types of switching devices such as an electromagnetic relay, vac uum tube device, transistor element and the like.

The operation of the fast acting solenoid in Fig. l is perhaps best understood by observing the sequence of events which occur when the switch arm 92 of the switch 79 in Fig. 2 is operated back and forth between the contacts 76, 8% on the one hand and contacts 78, 90 on the other. When the switch arm 92 is placed in the position shown in Fig. 2 engaging contacts 76 and 88, the coil 32 in Fig. l is energized. A magnetic field is established around the coil 32 which may extend to the left through the core 24 as indicated generally by the loops tilt) and 162. The cylindrical sleeve 28, having a much lower permeability than the disc member 54, diverts the magnetic lines of flux outwardly through the disc member 54. The lines of flux then travel outwardly in a transverse direction through the collar 16, back to the right along the portion 10 of the casing, then inwardly through the projecting portion 42, the pins 46 and 48, the bushing 44 and plunger 50 back to the core 24. Accordingly, the magnetic field from the coil 32 polarizes the disc member 54 and holds it tightly against the collar 16 and core 24 by the force of magnetic attraction. The flat annular member 14 serves to prevent magnetic lines of flux established by the coil 32 from entering the portion 12 of the casing. Since the flat annular member 14 inhibits the travel of magnetic lines of flux through the portion 12 of the casing, the disc member 56 is not magnetically polarized. The plunger 56, mounted for free movement longitudinally within the casing about the rod 52, is polarized by the magnetic field of the coil 32, and hence the plunger i? is drawn to the left until it engages the core 24. As a result the spring 62 is compressed between the plunger 56 and the disc member 54 as they are drawn into engagement with the core 24. The energy for holding the spring 62 in compression is thus supplied by the magnetic field from the coil 32, and thus it is seen how the fast acting solenoid is held in the position indicated in Fig. l representing one of its bi-stable states.

If the switch arm 92 in Fig. 2 is thrown to the right in engagement with the contacts 78 and 90, the coil 32 in Figs. 1 and 2 is de-energized simultaneously as the coil is energized. The magnetic lines of fiux represented generally by the loops 1653 and 162 in Fig. l collapse as the magnetic field represented generally by the loops 164 and 166 in Fig. 3 builds up. As the magnetic field indicated by the loops 166 and MP2 collapses, the spring 62 serves to thrust the plunger 56 and the disc 54 away from the core 26. The combined inertia of the disc 54, the rod 52 and the disc 56 is much smaller than the inertia of the plunger 5%, and the rod 5 2, the disc 54 and the disc 56 are accelerated fully to the left before the plunger Sil is hardly moved. Thus the rod 52 moves very rapidly to the left until he disc 56 is drawn into engagement with the core 26. The build up of the magnetic field represented by the loops 164 and 366 magnetically polarizes the disc and by the force of magnetic attraction this disc is held in engagement with the core 26. The magnetic field from the coil 34 establishes lines of flux which extend to the right in the core 26 as indicated by the loops 1124 and 3% in Fig. 3. The cylindrical sleeve 30, being more difiicult to magnetize than the disc member 56, diverts the magnetic lines of flux outwardly through the disc member 56. The lines of flux then travel upwardly in a transverse direction through the collar 18, back to the left along the portion 12 of the casing, then inwardly through the projecting portion 40, the pins 46 and 48, the bushing 44 and plunger 50 back to the core 26. Accordingly, the magnetic field from the coil 34 polarizes the disc member 56 and holds it tightly against the collar 18 and the core 26 by the force of magnetic attraction. The flat annular member 14 serves to prevent magnetic lines of flux established by the coil 34 from entering the portion 10 of the casing. Since the fiat annular member 14 inhibits the travel of magnetic lines of flux through the portion 16 in the casing, the disc member 54 is not magnetically polarized. The plunger 50 mounted for free moving longitudinally within the casing about the rod 52, is polarized by the magnetic field of the coil 34, and hence the plunger 56 is drawn to the right until it engages the core 26. As a result the spring 64 is compressed between the plunger 50 and the disc member 56 asthey are drawn into engagement with the core 26. The energy for holding the spring 64 in compression is supplied by the magnetic field from the coil 34, and thus it is seen how the fast acting solenoid is held in the position indicated in Fig. 3 representing the other of its bi-stable states.

Because the air gap between the disc 56 and the core 26 and the air gap between the plunger 50 and the core 26 are each greatest at the instant the switch arm 92 is thrown to the right in Fig. 2 and further because the magnetic field from the coil 34 is substantially zero at this instant, the magnetic polarization of the disc 56 is a minimum at this time. As the disc 56 moves to the left by decompression of the spring 6-2, the air gap between the core 26 and this disc diminishes. The equation defining the magnetic force of attraction on the disc 56 may be stated thus:

where K is a constant depending upon the parameters of the solenoid and D is the distance across the gap measured between the core 26 and the disc 56. Thus it follows that the force of magnetic attraction increases by a square function of the distance. This force serves to pull the disc 56 against the core 26 and hold it there against chatter 0r bouncing back and forth against the face of the core 26. It is desirable, therefore, to provide an initial magnetic force of attraction sutficiently large to prevent chatter or bouncing. For this purpose the condenser-s and 82 in Fig. 2 are provided. As soon as the switch arm 92 is thrown to the right in engagement with the contacts 78 and 90, the condenser 82 provides a large surge of current through the coil 34. This serves to cause a rapid build up of the magnetic field around the coil 34 in Fig. 3. By decreasing the time it takes the magnetic field from coil 34 to build up to a maximum value, the force of magnetic attraction on the disc 5-4 is likewise more rapidly increased. The compression of the spring 62 in Fig. 1 is greatest at the instant the switch arm 92 is thrown to the right in Fig. 2. The force of compression in the spring 62 decreases as the disc 56 approaches the core 26. However, the compression force of the spring 62 used to accelerate the disc 56 to the left is relatively large initially and provides a fast snap action in moving the disc 56 from its rightmost position to its leftmost position in engagement with the core 26. Accordingly, the increase in build up of the magnetic field in the coil 34 simultaneously with a decrease in the air gap between the disc 56 and the core 26 work cumulatively to provide an initial force on the disc 56 as it moves to the left in engagement with the core 26, thereby avoiding chatter or bouncing of the disc 56 against the face of the core 26.

The force of magnetic attraction between the plunger 5'!) and the core 26 is defined by the equation where K is a constant depending upon the parameters of the solenoid and D is the distance across the gap measured between the plunger 50 and the core 26. Thus this force of attraction increases as a function of the square of the distance and serves to pull the plunger 5!) against the core 246, compressing the spring 64 between the disc 56 and the plunger 50. The action of moving the plunger 50 against the force of the spring 64 takes place after the disc 56 and the rod 52 have completed their travel to the leftmost position with the disc 56 engaging the core 26. The magnetic force of attraction which draws the plunger 50 against the core 26 increases as the distance therebetween decreases. The force necessary to compress the spring 64 increases as the spring is compressed. Thus the increase in the magnetic force of attraction between the plunger 50 and the core 26 is sufficiently large to move the plunger to the right, thereby simultaneously compressing the spring 64 between the plunger and the disc 56.

If the switch arm 92 is again thrown to the left engaging contacts 76, 83 in Fig. 2, the discs 54, 56 and the plunger 59 are shifted from the positions indicated in Fig. 3 to the positions shown in Fig. 1. In the process the magnetic field of the coil 34 decays, and the spring 64 is decompressed; thereby the two discs are rapidly moved to the rightmost position with the disc 54 engaging the core 24. As the magnetic field around the coil 32 builds up rapidly with a surge of current from the condenser 80, a strong magnetic force of attraction is established between the core 24 and the disc 54 which prevents the disc 54 from bouncing back and forth against the face of the core 24. Shortly after this action takes place the plunger 50, delayed slightly because of its relatively large inertia, is drawn by a force of magnetic attraction to the core 24, thereby compressing the spring 62 between the disc 54 and the plunger 50.

Thus it is seen that if the switch arm 92 in Fig. 2 is thrown to the right engaging contacts 78 and 90, the rod 52 and discs 54, 56 are rapidly moved to their leftmost position as shown in Fig. 3, representing one stable state. If the switch arm 92 in Fig. 2 is thrown to the left engaging contacts 76 and 88, the rod 52 and discs 54, 56 are rapidly moved to their rightmost position as indicated in Fig. 1, representing another bi-stable state. Each time the switch arm 92 changes position, the rod 52 and the associated discs 54 and 56 rapidly change their position, and in a follow-up operation immediately thereafter the plunger 50 is drawn toward the polarized core, either core 24 or core 26 as the case may be, thereby compressing the associated spring 62 or 64. It is the followup action of compressing the associated spring and holding it in compression that makes possible the rapid movement of the rod 52 and its associated discs 54 and 56 to their new position when the switch arm 92 in Fig. 2 is changed. In one practical embodiment constructed according to the present invention, a load of approximately 15 pounds coupled to the rod 52 was actuated back and forth a distance of about 0.25 of an inch in several milliseconds. This time represents the period it takes the shaft 52 and its associated discs to change from one position to the other. The period for the plunger 50 to move from one position to the other is relatively greater.

What is claimed is:

l. A fast acting solenoid including a casing, first and second magnetic disc members engageable and disengageable with the opposite ends of said casing, a movable connecting rod mounting said discs adjacent the opposite ends thereof and axially arranged within said casing, a magnetic plunger mounted on said connecting rod between said disc members and movable with and relative to said rod, first and second substantially similar compression springs disposed between said plunger and the respective first and second disc members, first and second substantially similar electrical coils disposed within said casing, first and second cylindrical magnetic cores associated with the respective first and second coils and coaxial with the first and second springs respectively whereby upon energization of said first coil, adjacent portions of said casing, the plunger, the first core and the first disc member are magnetically polarized thereby magnetically drawing the plunger and first disc member toward each other and compressing said first spring therebetween until said first magnetic disc engages said casing and upon the alternate energization of said second coil, adjacent portions of said casing, the plunger, the second core and the second disc member are magnetically polarized thereby magnetically drawing the plunger and second disc member toward each other and compressing said second spring therebetween until said second magnetic disc engages said casing, the stored energy of said compressed spring in each instance serving to rapidly move said first and second disc members in a push-pull relationship from one bi-stable stationary position to the other in response to the alternate energization and de-energization of the first and second coils.

2. The apparatus of claim 1 wherein the casing is cylindrical, said cylindrical casing being constructed with two parts spaced from one another by a material that is difiicult to polarize magnetically, said two parts of the casing and said spacing material being formed into a unitary structure.

3. The apparatus of claim 2 wherein the cores associated with the first and second coils are separated from said casing by material which is ditficult to polarize magnetically, said cores and said two parts of the casing being constructed of material which is easily polarized magnetically.

References Cited in the file of this patent UNITED STATES PATENTS 2,292,478 Ray Aug. 11, 1942 2,437,639 Floyd Mar. 9, 1948 2,659,074 Alexander et al Nov. 10, 1953 2,832,919 Reutter Apr. 29, 1958 

